Tuesday, July 28, 2009

The next time someone cuts you off on your morning commute, don't be so quick to call the driver a jerk; you may have a reason to say thanks. According to the latest physics research, rule-breakers—drivers passing you on the wrong side or changing lanes too close to the intersection—actually help smooth the flow of traffic for the rest of us.

"The interesting finding is that if most of the people are law-abiding, and you have a certain amount of people who are breaking the rule, then you are actually getting the minimum chance of a [traffic] jam," said Petter Minnhagen, a physicist at Sweden's Umea University and an author of the paper published in the journal Physical Review E.

Physicists at the school uncovered this phenomenon while constructing a computer model of how a crowd of people move across a confined space, such as a pedestrian-only street. They divided the space into squares, like a chessboard, and randomly placed pedestrians in some of the squares. Like real people, the model pedestrians had a certain small probability of momentarily pausing, as if they had run into a friend or had bent down to tie a shoelace.

To make things more interesting, the researchers then tossed a few mavericks into the mix, who didn't follow the rules the other pedestrians used. The physicists ran the simulation over and over, each time boosting the percentage of rule-breakers. At first pedestrian deadlocks worsened. But as more and more rule-breakers joined the fray, something entirely unexpected occurred: traffic flowed best when only about 60 percent of pedestrians were obeying the rules.

Simple interactions of individual cars, people, or molecules add up to large patterns in a system. The high concentration of pedestrians in a small area increases the chances of a jam, but rule-breakers made the crowds spread out.

Morris Flynn, a University of Alberta professor who uses computational methods to study car traffic, agrees with the explanation. Because rule-breakers "carve out their own path," Flynn said, they dilute large concentrations of rule-abiders moving in the same way. He pointed out an example familiar to anyone who has driven on a two-lane road: breaking the speed limit to pass a slow vehicle prevents a long chain of cars from forming.

However, there is one rule you shouldn't break, according to a new analysis of how high-volume traffic flows along a highway. Cecile Appert-Rolland, a physicist at the University of Paris-Sud, looked at the tailing distances between cars traveling on a busy two-lane expressway in the suburbs of Paris. Most people have heard of the "three-second rule" for following distances; after the car ahead of you passes a point on the road, count to three. If you pass the same object before you get to three, you're following too closely. This time-based measure of the distance between cars is what Appert-Rolland terms the "time headway."

Her research showed that tailgating drivers were more likely than a non-tailgater to have a car in the lane next to them, so they weren't just speeding up in order to change lanes. She also found that these short time headways tended to extend across several vehicles, creating a platoon.

"We can identify at least seven or eight cars where they have time headways of half a second," she said. Considering that a driver's reaction time is about one second, these platoons are disastrous pileups waiting to happen. "If the first one brakes, the second one has to brake harder, the third one even harder, and the last wouldn't be able to brake hard enough."

So while unexpected behavior may help with congestion, always follow the three-second rule—because if you're tailgating, chances are you won't be the only one.

The thing about these "platoons" is that when you're driving that close you're not just watching the car in front of you but the car in front of him. You actually end up monitoring a couple of cars ahead. So if you see something happening to the car 2,3 or 4 cars ahead you start easying off and you have more time to brake when the mud really hits the fan. I'm sure alot of drivers drive this way. Just a thought.

Interesting article. However I think the term "jerk" needs to be defined a bit better. Here in the San Francisco Bay Area, as I'm sure elsewhere, people are in the habit of driving in the fast lanes, regardless of how fast their going. Sure they may be going the speed limit, but invariably they're holding up traffic.

According to this article, the jerk would be the person passing on the right, however my contention is that the person holding up traffic in the fast lane is actually the jerk.

The rule is generally known as "slower traffic, keep right", but it's rarely followed, and never enforced. Having driven in Germany for a few years, this rule (Rechtsfahren!) was always strictly adhered too, and seemed to improve traffic significantly.

A friend of mine had the opportunity to ask a buddy of his about this. His friend got on the freeway and immediately moved across all four lanes to the left. He then cruised along at the speed limit, while frustrated drivers were passing him on the right. His reason? "It's smoother." No joke.

This kind of self-centered approach to driving, to say nothing of the level of distraction we all deal with is a really bad combo.

I'm disconcerted that Appert-Rolland is using that discredited meme that "a driver's reaction time is about one second". It's actually a half-second or less unless the driver is distracted. Furthermore, there are very few circumstances where the front driver completely slams on the brakes. Very few.

Lastly, the three-second rule means that most people would never be able to enter the highway. If you attempted to merge, you would break everyone else's three second rule behind you and everyone would have to slow down to let you merge. So you can't say "never" because your highway would be at capacity in no time at all.

The left lane in a multi-lane road is for PASSING (and turning left). Need to overtake a slower moving vehicle? Move into the left lane (when its clear to do so - you did check for someone approaching from the rear, yes?), pass the slower vehicle, THEN MOVE BACK TO THE RIGHT. Yet a large percentage of drivers here in the U.S. make a bee-line for the left lane as soon as the get on the road. These mindless, ignorant people in the left lane are the jerks. Get them out of the left lane and (1) traffic flows MUCH better and (2) states can stop passing these ridiculous "aggressive driver" laws that target those of us who actually know what the left lane is for.

As others have commented, it's not "passing on the wrong side", it's "driving on the wrong side." The "rule breaker" here is the driver who thinks the left lane is the "fast lane" and not the "passing lane". There is a huge ideological difference between the two.

I try to drive on the right, and move left to pass. If I pass you on the right, it's because you're in the wrong lane. Move over.

chrisr Thank you, thank you, thank you! I was beginning to suspect I was the only one who noticed how Nor Cal drivers in general seem to be oblivious to the fact that they are piloting 4000lbs of steel at 65+ mph.

Many drivers are in their own little worlds, paying absolutely no attn to the cars around them and minimal attn to the road ahead of them.

If there's no one in front of you, why not move over?

Austin, Texas they seem to get it. Haven't driven there a whole lot, but here are my impressions: Traffic keeps moving, even on two lane highways with people driving at varying speeds. The reason is they use the left lane as a passing lane and generally stay to the right (except for the occasional cowboy flying in the left lane). People check their mirrors and move over if someone is coming up quick behind them. It's beautiful.

Personally, I prefer aggressive drivers who pay attn over slower drivers with their heads up their asses. Speeders tend to be more aware of the road b/c they are looking for cops or looking for the easiest way through the next group. While there are some extraordinary jackasses out there who are definitely exceptions to this general rule of thumb, in general I prefer to drive with drivers who are actively driving rather than passively trying to get from here to there (more often than not while chatting, texting, listening to music, messing with a gps, applying makeup, etc.).

Slow does not equal safe. To Chris's point, many people consider fast drivers to be the "jerks." However, I wholeheartedly agree that the self-centered drivers are much more of a problem than fast drivers.

1. Pedestrians are not cars. Two people bouncing off one another does not equate to two cars doing that.2. The simulation called for 40% to break the rules for pedestrians. Pedestrians rules are looser and have less consequences in breaking them. If 40% of cars say, disobeyed traffic lights and stop-signs we'd have far more crashes.3. There's only so much traffic can spread out on a highway. Driving on the grass isn't really an option for cars, unlike pedestrians.4. At the speeds pedestrians move, reaction time can be a negligible factor. As the tailgating research reminds us, reaction time is a crucial factor in car pileups and collisions.

Generalizing the pedestrian simulation to automobile behavior is irresponsible, if not just absurd

Platoons are caused by the lack of a gradient in speed between two lanes, primarily because the jerk in the "passing lane" is not making a timely enough pass.

This stems from an insane ticketing/insurance system in which our tax dollars go wasted paying policemen to be forced to pull people over to fill a quota (rather than doing real police work), and our insurance companies gladly and heavily punish drivers based upon this.

In the state of MA, a simple 2nd speeding ticket (think 67 in a 55) means a 30% insurance surcharge for 3 years, then %15 for another three after that. This can mean as much as $1500 - $2000 out of pocket.

The driver in the passing lane is usually not paying attention (on the phone) or more likely "afraid" to speed up enough to complete a pass.

That's another issue. I can't see a damn thing from my Ford Focus when any SUV is ahead of me. I end up depending on the SUV driver's reaction time and style, which is, generally speaking, horrid.

And before anybody flames me for SUV-bashing and generalizing, research the countless studies that have found time and again that SUV drivers are statistically uncomfortable with their driving ability and purchase the vehicle as a subconscious crutch.

BALONEY !!I used to work in an office overlooking a busy freeway ... and it was a great entertainment seeing how the JERKS CAUSED THE TRAFFIC TIE-UPS by zooming ahead and slamming on the brakes, zooming ahead and slamming on the brakes ... while the lanes where drivers kept a steady pace rarely made traffic come to a complete stop and always moved ahead faster

I haven't been driving for long enough to make an educated enough statement, but I personally believe that the left lane SHOULD generally be the fast lane.

I drive on a major Houston freeway every day. I get on in the morning and (saftely) merge all the way to the left A.S.A.P. and continue down the road for several miles until I get past the exit before the one I need. Then I get over and exit normally.

I do this on this particular freeway because traffic in the middle & right lanes always seem to go slower then the speed limit, and also because the way the exit and entrance ramps are set up. It seems like it is literally impossible for most people to speed up enough when trying to enter the freeway that it causes such a backlog in the right lane.

I use my blinkers 99% of the time and will move to the right lane to let someone pass me if the situation permits. But I still believe that on a freeway (but not any other road), the left lane should be reserved for those of us who are willing and able to push past the stupid people doing 5 (or more) under the speed limit. And its fairly common unwritten knowledge that unless there is a cop around, the left lane is for 70+ mph, unless traffic doesn't permit it.

I found a lot of the comments here rather interesting. First, that the left lane is for passing. I believe, and may be wrong, that those who talk about the fast lane mean the freeway. I don't know about anyone else, but I don't really want to cross five lanes of traffic so I can a group of cars going ten miles under the speed limit, and then go all the way back to where I began on the right. I prefer to drive in the left lane. Which has never caused me any problems, since anyone wanting to pass me is going 30 miles over the speed limit anyway. Hehe

I think it's worth noting how stylized the pedestrian rules are in this study. I haven't sprung for the full paper, but I find myself wondering if maybe the rules themselves could have been changed in such a way as to make rule abiding the optimal "solution."

Rule abiders only bunch if they chose to do so. They teach you to prevent bunching up so if you abide by the rules and THINK bunching up doesnt happen. Aside from the blatantly obvious issues to anyone that has to drive extensively there is a huge difference between walking people and car traffic. How many people do you know that walk at 65-85MPH? None. Speeding isnt the issue. Its being cut off, premature lane changes (not just intersections), etc, or worse wrecks. They all cause massive slowdowns in traffic and bunching. I see it every day where people cut each other off and it results in a 30-40 car line to slow down and bunch up losing about 10-15mph and typically, if you are very lucky, it recovers over about 3-5 miles. Otherwise the line of cars continued the speed safely and consistently indefinitely. The topic is misleading. It should say "foot traffic". Tailgating is by far the worse form of traffic violation and they need to bust more people for it rather than speeding. You can speed smart. Tailgating is always stupid.

This means get out of the way of faster people. Change lanes if you can free up a lane for someone else to get out of the slow-lane. If someone is waiting for you at a stop sign, speed up to get out of their way faster.

#2) Don't slow down for anyone else.

This means if someone is in front of you going slower, change lanes and go around them, don't match their speed. Never slow way down to let someone in... you are helping one person and pissing off the 50 people behind you! Always accelerate to change lanes, never break to get behind someone.

Oh I see, my comment gets deleted because I don't think the correct way politically?

I know it's not for swearing because I checked for other comments that swore, and found swearing in other comments, which had not been deleted. So the only logical conclusion is you hate SUV's too, and are part of the "tolerant", "free speech" crowd that only allows the correct "free speech", and is only tolerant of your viewpoint.

Because you are unaware that there is no one in front of you and people all around you.

"According to this article, the jerk would be the person passing on the right, however my contention is that the person holding up traffic in the fast lane is actually the jerk."

"…I prefer aggressive drivers who pay attn over slower drivers with their heads up their asses. Speeders tend to be more aware of the road b/c they are looking for cops or looking for the easiest way through the next group."

1) Brakes should not have to be used on highways. If you are using the brakes, assuming there isn't a traffic jam already, you may have just started one, idiot. Learn to downshift, change lanes, or speed up, but please stop using your brakes on the highways!!! IT CAUSES ALARM FOR THE DRIVERS BEHIND YOU.

2) If there is a car in your rear view and you are in the left lane, speed up and get out of the damn way. SHARE THE ROAD!

chrisr: actually, the Bay Area has completely terrible pavement, built on individual concrete blocks instead of an aggregate bed. The best they can do is grind it flat every couple years and re-pave, but it gets bumpy pretty quickly. The car-pool lanes were generally built a few years later, and they were done properly; as a result, the inside lanes often do have a smoother ride.

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Anonymous and other assholes: Oh, the left lane is the "passing" lane and not the "fast" lane? Well, then, PASS ALREADY. Then GET OUT OF THE WAY so that *I* can pass YOU.

Of course this only works in countries where most people abide to most rules :)Probably won't work in cities such as Bombay Jakarta, or most east asian cities that makes cab drivers in NYC look like the most decent drivers out there.

Wow. Lots of clueless people commenting here and many smart ones, but it's very simple: You stay to the far right most lane unless you are passing. PERIOD.That allows "faster" traffic to always pass you where they should, on the left.

Think about this. What is "fast" to you? Is that the same thing as "fast" to me? No, that's a subjective argument. No one is going to be right.

There are NOT "fast" lanes and "slow" lanes. There are PASSING lanes and TRAVELING lanes.

Everyone can argue over "fast" or "slow". NO ONE can argue over "PASSING" or TRAVELING. You either are you are aren't PASSING, and if you aren't PASSING, then MOVE THE ^%&!# OVER!!!!!!!!!!!!!!!!

There's one area where this has definitively proven to be true. It's called "late merge". When you're on a multilane highway and a lane is ending 1/2 mile ahead (either because the lane ends or because there's an accident or work zone ahead), DON'T be nice and merge left immediately!! Instead, drive all the way to the end and THEN merge.

I know some people think those "late mergers" are heartless jerks, one step below child rapists. But it actually makes a lot of sense when you think about it in terms of real estate. If every does an early merge, you've got a 3-mile backup in one lane and a whole bunch of wasted real estate in the empty lane. If everyone does a late merge, now you've got two lanes that are each only backed up for 1.5 miles.

PennDOT actually experimented with encouraging this a few years ago. They had a major construction project that eliminated one lane on each direction of an interstate. In one direction they did the standard "right lane ends 1 mile", "right lane ends 1/2 mile", etc.

But in the other direction they put up special signs saying "use both lanes to merge point". At the merge point, the sign said "merge here take your turn". The result: significant, major improvements in how long it took everyone to get through.

This is unsafe under real light traffic flows (say, 3:00 am) when your sudden, late merge could cause an accident. But when it's heavy traffic and there will be a backup no matter what, late merge makes a lot of sense.

So next time, do it. Ignore the honks and the fingers; you're actually helping society out.

I bike my way to office and my bit of social service enroute is to squeeze into the next available gap on road. But I (uninformedly) judge whom I'm passing by the way he/she is driving lest I get killed for the noble cause.

In India the rule is 'drive on the left of the road'. In Bangalore our rule is 'drive on what's left on the road'!

I'm also up here in Toronto. If I'm passing you on the right (in NA), then you are in the wrong lane!

The other thing which ticks me off is that the current speed limits are designed for the lowest common denominator, "mediocre drivers with wandering attention, bald tyres and slippery roads".. Actually they are designed for revenue, and no longer has anything to do with safety..

I think it's safe to say that most of the people interested in this article (enough to post a comment) already know the rules and try to obey them while the jack animal in the left lane, going 5 under, with his left blinker on (for miles!)...couldn't care less about the rules or the fact they're creating dangerous situations behind them.

In Sweden it's illegal to NOT move over for an overtaking vehicle, even if that vehicle is breaking the law (or just being a total douche) by overtaking. So yes, the slow driver in the left lane is the jerk. Since most roads have only one or two lanes in each direction this is a very necessary rule.

As an auto racer and high performance driving instructor, I can tell you most people mistake being cautious for being safe. Driving is largely counterintuitive and much of what is taught in preparation for receiving one's driver's license is not wrong, it's dangerous!

far left lane sometimes is carpool lane, reserved for the few who qualify, and some of course are "jerks" who, yes, drive the speed limit or less, blinker on . . . some good tips in this sequence: late merge, looking ahead beyond the car in front of you, avoiding use of brakes on the freeway

Regarding the study, it's interesting. But I have to throw up one cautionary note. Nonlinear dynamic (sometimes called "chaotic") systems - of which traffic is basically one - often exhibit "pockets" in parameter space where the behavior becomes counterintuitive, then intuitive, then perhaps "random seeming", etc., as that parameter is changed. I'm curious what other domains appeared when the rule-breaker rate was higher or lower than that interesting spot at 40%. I didn't see a link to the actual study - maybe it's subscription only (most journals still are). So, as someone pointed out below, the application to the real world may be somewhat different than what you see printed above.

Regarding the FAST LANE/PASSING LANE debate... this is a false dichotomy, and another example of our annoying human need to reduce a continuous variable into binary to simplify the world for our little brains. In reality the description for what various people do in that lefthand lane exists on a continuum. At one end of the spectrum we have the "clean pass". Someone moves into the left lane, speeds up, and then moves immediately back to the right just in front of the car they were trailing. At the other end of the spectrum we have the proverbial Sunday driver hanging out in the left lane forever and going slower than every other car on the road. But in busy interstate traffic situations, the vast majority of the left-lane residents are doing something IN BETWEEN those two extremes (yes, I know this strains your black-white world to contemplate, but it's actually true). Someone moves into the left lane because he is going *generally* faster than the cars in the right lane, and begins slowly but steadily passing one after another of the right lane vehicles. But lo - then along comes one of the "special speeders" (several of whom have posted below), and she/he deems (in his/her absolutist judgment) that that car is not passing enough people per every ten seconds of time, and should therefore disrupt the crowded right lane in order to fold back in. What I'm saying here isn't that one of them is definitively right and the other's wrong, but that things do not fit neatly into "you're fouling things up and I'm not".

BOTTOM LINE: Get out of the fast lane if people are passing you on the right. Slow cars that stay in the passing lane create artificial delays/backups and decreases the level of service on the roadway ARTIFICIALLY. The average speed of the vehicles behind the jackass is decreased significantly due to only one vehicle. Add another 10 or 15, and you get an artificial traffic slowdown. There may not be another car in front of them for a mile, but there can be 15 or 20 cars packing in behind them awaiting an opportunity to pass the jerk.

Tailgating seems to be a phenomenon that has missed the UK. I am a driving instructor and even when i took my driving test ('ahem'.. years ago :)) we were taught the 3 second rule. I teach it to my students now. Trouble is, when on the motorway, you leave a space that big and someone is just bound to jump from the inside lane and fill it!!

We all make mistakes while driving - but be fair enough to admit a mistake by apologizing. This will take out some of the stress factor in those situations. Use turn lights whenever make a lane change or turn. If the car behind you has to hit the brakes hard to avoid an accident because you made turn without using the turn lights can even result in an accident.

Anon 5:49 hit the nail on the head. When traffic is congested, different rules apply. If all drivers instantaneously pass on the left and merge back into the right lane, assuming a constant distance between cars, the throughput of the highway is halved. If cars use both lanes, congestion is eased and throughput is increased. Insisting that all but a few statistical outliers clog up the right lane is not going to ease congestion. And, of course, as exemplified by the ridiculous comments on this page, 90% of the population believes that they are the outlier, which makes such an arrangement unsustainable anyway.

Unfortunately, I do have to admit that tailgating, while not beneficial at all to the individual, is socially optimal excepting accidents. If the average distance from front bumper to front bumper can be decreased by half, the throughput of the road doubles. Still, it's reckless, unnecessary, and stressful for all involved.

In the end, I don't care what the research says. If someone is, god forbid, actually going the speed limit in the left lane, there's no need to tailgate or pass them on the right. Think about your loved ones and their loved ones and just chill out.